High temperature polyimides from 2,3-diacylsuccinic acid diester with diamines

ABSTRACT

Polyimides which are stable at temperatures up to about 450* C. to 500* C. and which are useful for high temperature applications are prepared by reacting 2,3-diacylsuccinic diesters with diamines in a 1:1 molar ratio. Polyimides are also produced by reacting 2,3-diacylsuccinic diesters with diamines in a 2:1 molar ratio to form bis(pyrrole-3,4-diesters), hydrolysing the tetraesters to form the corresponding bis(pyrrole-3,4dicarboxylic acids), dehydrating the tetracarboxylic acids to form the corresponding bis(pyrrole-3,4-anhydrides), reacting the dianhydrides with aliphatic or aromatic diamines to form poly(amic acids), and thermally cyclizing the poly-(amic acids) to form polyimides. Alternatively, the aforementioned tetraesters, tetracarboxylic acids, and dianhydrides can each be reacted with bis(orthophenylenediamines) to form poly-(imidazopyrrolones) which are also useful for high-temperature applications.

United States Patent 1 1 Stackman et a1.

1 1 July 29, 1975 175] Inventors: Robert W. Stackman, Morristown,

N..l.; Donald W. Sargent, Schenectady, NY.

1731 Assignee: Celanese Corporatlon, New York,

122] Filed: Aug. 24, 1973 1211 Appl. No.: 391,396

Related U.S. Application Data [63] Continuation-impart of Ser. No.143,674, May 12,

1971, abandoned.

[52] US. Cl. 260/78 A; 117/161 P, 260/30.8 R, 260/47 CZ; 260/47 CP',260/63 N", 260/65;

260/78 R; 260/78 TF; 260/326.25', 260/326.46

[51] lnt. Cl C083 20/04; C08g 20/20 [58] Field of Search 260/78 A, 78TF, 47 CZ, 260/47 CP, 63, 65, 78 R [56] References Cited OTHERPUBLICATIONS Hollins, Synthesis of Nitrogen Ring Compounds, 1924, pp.28-33. Piattelli et 211., Chemical Abstracts, Vol. 62 (1965) col.1621-1622.

Stern et al., Chemical Abstracts, Vol. 27 (1933) p. 4796.

Vasserman et al., Chemical Abstracts. Vol. 33 (1939) col. 7665-7666.

Knorr, Annalen der Chemie, 1886. B'ande 236, pp. 296-317.

Primary Examiner-Haro'ld D. Anderson [57] ABSTRACT Polyimides which arestable at temperatures up to about 450 C. to 500 C. and whichare usefulfor high temperature applications are prepared by reacting 2,3-diacylsuccinic diesters with diamines in a 1:1 molar ratio. Polyimidesare also produced by reacting 2,3- diacylsuccinic diesters with diaminesin a 2:1 molar ratio to form bis(pyrrole-3,4-diesters), hydrolysing thetetraesters to form the corresponding bis(pyrrole-3,4- dicarboxylicacids), dehydrating the tetracarboxylic acids to form the correspondingbis(pyrrole-3,4- anhydrides), reacting the dianhydrides with aliphaticor aromatic diamines to form poly-(amic acids), and thermally cyclizingthe poly-(amic acids) to form polyimides. Alternatively, theaforementioned tetraesters, tetracarboxylic acids, and dianhydrides caneach be reacted with bis(orthophenylenediamines) to formpoly-(imidazopyrrolones) which are also useful for high-temperatureapplications.

9 Claims, No Drawlngs 1 a 2 HIGH TEMPERATURE POLYIMIDES FROM atureapplications. 2.3-l)lACYLSUCCINlC ACID DIESTER WITH Another object is toprovide novel compounds which DlAMlNES are useful as precursors in theproduction of the novel 4 polyimides and poly-(imidazopyrrolones) ofthis inven- CROSS REFERENCE TO RELATED APPLICATION ion- This is acontinuation-in-part ofU.S. application Ser. 5 Yet another object is toprovide processes for pro- No. 143.674 filed May i2. [971, nowabandoned. ducing the aforementioned novel polyimides, poly- Theinvention relates to thermally stable polymers. (imidazopyrrolones). andprecursors thereof. More particularly, it relates to thermally stablepolyi- These and other objects as well as advantages of the mides andpoly-(imitlazopyrrolones) and to processes 10 present invention can behad by reference to the folfor producing same from novel precursors. nget ed description and Claims.

it is known that cyclic lmides, such as succinimide Broadly. the aboveobjects are achieved according to and glutarimide, as disclosed in U.S.patent No. the present inventlon by selectively reacting the ke-3.309.3( 5. can be made from succinic anhydride and tonic carbonylgroups ola 2,3-diucylsuccinic diester (l) glutaric anhydride.respectively. It is also known that 5 with B diflmine in 8 ltl molarratio to o m t e anhytlrides can be prepared from carboxylic acids, andsub ti uted-py ro e-3. -dieste ROOC c H N-R"NH N R" NH 2 2 2 ROOC RoocRI 7 RI that such acids can be prepared from esters. However, Uponheating, the pyrrole-3,4-diester (lll) undergoes it s t to o been knownthat 35 intermolecular amidation-cyclization to form polyidiacylsuccinicdiesters can be utilized for the producmides comprising recurring unitsof the formula (IV):

tion of useful polyimides, and poly(imidazopyrroltisafeature ofthepresent invention that polyimides loncs). can also be produced byselectively reacting the ke- Therclore, it is an object of the presentinvention to tonic carbonyl groups ofl with ll in a 2:l molar ratioprovide novel polyimides and polyto form a bis(pyrrole-3,4-diester) (V):

(imidazopyrrolones) which are useful for high temper- 55 2 lll---'---""'- 3.897.402 3 4 The (pyr -3. -di is en ydr y d 10 Thebis(pyrrole-3,4-anhydridc) (VII) is reacted with a form thecorresponding bis(pyrrole-3,4-dicarboxylic s cond diamine (Vlli) to forma poly-(amic acid) comacid) (Vi): prising recurring units of the formulaIX, which is then V hzdrolxsis which in turn is dehydrated to form thecorresponding f y fy form a Polyimide Comprisingbi5.(pyrro|e.34.ahydride) v11 20 curring units of the formula X:

V" +H2N R", NH,

VI dehydration o N RII o Vlll HNOC CQNH- R" N N cyclizaiion HOOC CQQH R!RI 0 o N N R" N n Another feature of the present invention is that the.tetraesters (V) tetracarboxylic acids (Vl). or dianhydrides (Vll) canbe each reacted with a bis(orthophenylene diamine) (Xl) to form certainladder-type high-temperature polymers referred to hereinafter as poly-(imidazopyrrolones) comprising recurring units of the formula Xll:

or RH" VII Xll

Each of the foregoing compounds is described more and the like. R is ahydrogen substituent or an organic substituent (including unsubstitutedand substituted. saturated and unsaturated alkyl and aryl substituents)of between about 1 and about l0 carbon atoms. and preferably a loweralkyl :substituent of between about I and about 6 carbon atoms such asmethyl. ethyl. and the like.

The initial step of this two-step procedure can be fully hereinbelowtogether with the process conditions conveniently conducted in thepresence of a suitable necessary for effecting each step.

1. Formation of the 2.3-diacylsuccinic diesters (l) In this knownsynthesis, an acylacetic ester is conventionally reacted with an alkalimetal or alkali metal alcoholate (formed by reaction of an alcohol suchas methanol. ethanol. or tert-butanol with an alkali metal such assodium. potassium. or lithium) to form an alkali metal salt. which onfurther reaction with a halogen alkali metal alcoholata) l'tUlOgQn 2ROOC alkali metal (or organic solvent such as an alcohol or aromatichydrocarbon (e.g.. benzene, toluene) and initially at a temperature ofbetween about 25C. and about C. Thereafter, during this step of theprocedure. the mixture is heated at reflux. during which time hydrogenis evolved if the reaction is conducted with an alkali metal or alcoholis removed if the reaction is conducted with an alkali metal alcoholate.

In the second step of the synthesis. the mixture or slurry of the alkalimetal salt of the acylacetic ester is ROOC wherein R is an ester-formingsubstituent, desirably an organic ester-forming substituent of betweenabout i and about l0 carbon atoms. and preferably a lower alkylsubstituent of between about i and about 6 carbon atoms such as methyl.ethyl. propyl. iso-propyl.

ROOC

cooled to about 40-60C. and an equimolar amount of a halogen. such aschlorine, bromine or iodine. is added in small portions. After theensuing coupling reaction is completed. the mixture is allowed to standat ambient temperature and filtered to remove precipitated alkali metalhalide. Evaporation of the filtrate yields the product which can bepurified by conventional means, e.g., by crystallization.

According to the above procedure, for example, if the starting materialis ethyl acetoacetate, the resulting product is diethyl2,3-diacetylsuccinate.

The resulting 2,3-diacylsuccinic diester (l) is then reacted with asuitable diamine to form polyimides or bis(pyrrole-3,4-diesters) asdescribed below.

2. Formation of the N-substittited pyrrole-3,4- diesters (lll)N-substituted pyrrole-3,4-diesters of the type lll are producedaccording to the following reaction:

H ROOC Q ROOC Q ROOC l ROOC ROOC

N ---NH ROOC lll wherein R and R are as defined heretofore and R" is analkylene substituent of between 2 and about 10 carbon atoms (e.g.,ethylene, trimethylene, and the like), and arylene substituent (e.g.,phenylene, and the like), a biarylene substituent (e.g., biphenylene andthe like), a diarylene substituent (e.g., diphenylene ether, diphenylenesulfone, diphenylene amine, and the like) or a covalent bond. Examplesof diamines (ll) suitable for use in the present invention includehydrazine, ethylene diamine, trimethylene diamine, para-phenylenediamine, benzidine, di-(para-aminophenyl)ether, di- (paraaminophenyl)sulfone, di-(para-aminophenyl) amine, and the like.

The reaction ofl with ll to give lll is conducted according to thepresent invention by contacting them in a molar ratio of no more thanabout l:l, respectively. Molar ratios substantially greater than aboutltl will result in a product of lower purity. Preferably, 1:1 molarratio is used. Such contacting is desirably conducted in a suitabledehydrating medium, e.g., glacial acetic acid and the like. The reactionis generally conducted at an elevated temperature. more particularlyheat-- between about 50C. and about l25C., and preferably at theatmospheric reflux temperature of the system. During the reaction, wateris evolved and can be removed by conventional means, e.g., bydistillation. The resulting N-substituted pyrrole-3,4-diester (H1) isisolated by conventional means after the dehydration reaction iscompleted. This material can then be polymerized to form polyimides ofthe type IV as described below.

3. Formation of the polyimides (lV) N-substituted pyrr0le-3,4diesters(lll) undergo thermal polymerization to form polyimides (W) as shown inthe following equation:

N- R" NH2 This transformation is accomplished by heating lll above itsmelting point at a temperature which is generally above about C., moreparticularly between about l25 C. and 300 C., and preferably betweenabout C. and 200 C. for a time sufficient to form the desired polymers.in most instances the heating time will range between about 30 minutesand ten hours, preferably one to five hours. It is desirable to bring[I] to the reaction temperature gradually; once the desired reactiontemperature is attained, it is maintained thereat for a period of timedepending on the degree of polymerization desired, a longer residencetime toward the right (i.e., in favor of the polyimide). Upon completionof the reaction, the product can be isolated by distillation of solvent.The number of structural units in the polymer chain (i.e., the polymerchain at one end and a pyrrole3,4-diester substituent at the other end.

4. Formation of the bis(pyrrole-3,4-diesters) (V): The preparation ofthese intermediates is achieved length) is determined by the value of n,which value is 5 according to the following equation:

ROOC Q g H N- R" -NH ROOC R' RI ROOC COOR N R" N ROOC I COOR R R in turnreflected by the inherent viscosity of the poly- 40 wherein R, R, and R"are as defined heretofore.

mer. Generally, polyimides (lV) produced according to the presentinvention have inherent viscosities of between about 0.l and about 3.0,and preferably between about 0.16 and about 2.0. These inherentviscosities are determined on solutions of O.l gram of polymer/lOOmilliliters 97% H 80 at C.

lt is a feature of the present invention that, by use of theabove-mentioned polymerization temperatures for the reaction between 1and ll in a l:l molar ratio.isolation of the intermediate monomer (lll)can be avoided. thereby yielding polyimide (lV) directly by reactionbetween l and ll. Using this approach. it is preferred that the mixtureof monomers l and ll be brought slowly to the desired polymerizationtemperature. e.g.. over a period of several hours.

lt is a further feature of the present invention that polyimides (N) canbe produced by applying a solution of ill a solution ofl and ll in asuitable solvent (e.g., of the type described above) onto a surface andsubsequently heating or baking the surface at the above-indicatedtemperatures to effect polymerization and to remove solvent. in thisway, there is obtained a useful and desirable film or coating of IV onthe aforementioned surfacc. The polyimides (W) of the present inventionare generally terminated by free amino substituents andpyrrole-3.4-diester substituents in equal amounts. That is,statistically. each molecule of polyimidc (IV) will generally have afree amino substituent The reaction ofl with ll to give V is conductedaccording to the present invention by contacting them in molar ratios ofat least about 2:], respectively, and preferably at a molar ratio of2:l, respectively. The reaction is conducted at elevated (i.e.,effective) temperatures, desirably between about 50C. and about l50C.,and preferably at the atmospheric reflux temperature of a suitabledehydrating medium. such as glacial acetic acid and he like. During thereaction, water is evolved and can be removed by conventional means,e.g., by azeotropic distillation. The resultingbis(pyrrole-3.4-dicarboxylic ester)(V) can be isolated by distillationof solvent.

lt is essential to the success of the present invention that thereaction between I and ll be conducted in molar ratios which are eitherno greater than about l:l respectively (whereby III is produced) or lessthan about 2:1 respectively (whereby V is produced). The use of molarratios of l to ll of between substantially greater than about l:l andsubstantially less than about 2:1 will tend to result in undesirablemixtures of III and V.

The bis(pyrrole-3,4-diester) or tetraester (V) is converted to thecorresponding tetracarboxylic acid (Vl) by the hydrolysis reactiondescribed below.

5. Formation of the bis(pyrrole-3. dicarboxylic acids)(Vl) Thetetracarboxylic acids (V!) are formed from the tetraester (V) byhydrolysis according to the following wherein R, R and R" are as definedheretofore.

This hydrolysis reaction is carried out by contacting V with an aqueousbase such as aqueous alkali (e.g., NaOH, KOH, etc.). The reaction ispreferably conducted in a solvent such as water or an aqueous lower RIRI HOOC COOH 2HZO N R N HOO COOH II VI R a O (O O N R N O v" O R! R!alcohol such as aqueous ethanol. The reaction is preferably conducted atthe atmospheric reflux temperature of the system and the excess alcoholand alcoholic by-product can be removed by distillation. When all thealcohol has been removed, the tetracarboxylate salt is neutralized withmineral acid and the precipitated tetracarboxylic acid (VI) is recoveredby filtration with purification as desired (e.g., recrystallization froma suitable solvent).

COOH

The tetracarboxylic acid (Vl) is then dehydrated to form thebis(pyrrole-3,4-an1hydride) (Vll) as described below.

I) OH- 2) H 0 C OOH 6. Formation of the anhydrides)(Vll):

In this step, the tetracarboxylic acids (Vl) are dehydrated to form thecorresponding dianhydrides (Vll) according to the following equation:

bis(pyrrole-3,4

wherein R and R" are as defined heretofore,

This reaction is carried out by heating Vl under dehy drating conditionsas in a drying tube or with a dehydrating agent to remove water and formthe dianhydride. In a preferred method, Vl is contacted with an excessof acetic anhydride at reflux temperature from about 10 to about 50hours to produce the dianhydrides (Vll). The resulting precipitatedproduct is then removed by filtration and conventionally purified as(amic acid) (IX), as described below.

7. Formation of poly-(amic acids) from bis(pyrrole- 3,4 anhydrides):

In this aspect of the present invention, the dianhydride (VII) isreacted with a diamine (VIII) to produce a poly-(amic acid)(lX),according to the following The number of structural units in the polymerchain (i.e., the polymer chain length) is determined by the value of n,which value is in turn reflected by the inherent viscosity of thepolymer. Generally, poly-(amic acids)(lX) product according to thepresent invention have inherent viscosities of between about 0.15 andabout 3.0, and preferably between about 0.16 and about 2.0. Theseinherent viscosities are determined on solutions of 0.1 grams ofpolymer/I00 milliliters 97% H at 25C.

The reaction is conducted by contacting Vll with VII] in about a l:lmolar ratio in a suitable solvent. such as dimethylformamide,N,N-dimethylacetamide.

equation: dimethylsulfoxide, hexamethylphosphoramide, N-

+ il l-R' dill;

R! RH! 0 It 0 HN N N R" HOOC COOH L IX wherein R and R are as definedhereinabove, n is a methylpyrrolidone or any other condensationpromotingsolvent for about one to eight hours at ambient temperatures and above.Temperatures of between about 40C. and about 75--lO0C. are preferred;temperatures of above about C. result in formation of polyimides (X).After the reaction is complete, the solvent can be removed and theresulting solid is recovered and purified. Alternatively, the solventcan be retained to permit further processing as desired. The product isfound to be a polyamide with pendant carboxyl groups. During thereaction, ring closure to the imide occurs to some degree depending uponthe temperature at which the reaction is carried out and therefore theresulting product is generally a mixture of the two compounds. As shownbelow, however, the poly- (amic acid)-polyimide mixture can be easilyconverted to the polyimide (X).

8. Formation of polyimides (X):

As set forth in the following equation, the poly-(amic acids) (IX), whenheated, are converted to the corresponding polyimide (X):

hoot

wherein R, R" and R' and n are as defined heretofore.

This reaction is effected by heating the poly-(amic acid) (lX) at atemperature of above about l00C. and preferably between about 100C. andabout 300C. The reaction can be conducted, partially at least, in thepresence of a suitable high boiling solvent if desired, such asdimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, and hexamethylphosphoramide. The reaction can be completed bycontinued heating to remove solvent and by-product water.

The number of structural units in the polymer chain (i.e., the polymerchain length) is determined by the value of n, which value is in turnreflected by the inherent viscosity of the polymer. Generally,polyimides (IV) produced according to the present invention haveinherent viscosities of between about 0.15 and about 3.0, and preferablybetween about 0.l6 and about 2.0. These inherent viscosities aredetermined on solutions of 0.1 gram of polymer/100 milliliters 97% H 80at 25C.

It is, of course, to be understood that by use of the highertemperatures, isolation of the intermediate poly- (amic acids) (lX) canbe obviated, thus yielding X directly by reaction of Vll with Vlll.Thissreaction however must be conducted at temperatures of about l0OC.or above.

ROOC

ROOC

COOR

+ 2nH O The conversion of the poly-(amic acids) (lX) to the symmetricalhead-to-head polyimides (X) posesses 25 the same features and aspects asthe conversion of nsubstituted pyrrole-3,4-diesters (ill) to thelikewise symmetrical but "head-to-tail" polyimides (IV). as discussedheretofore.

9. Formation of poly-(imidazopyrrolones) (Xll):

It is a further feature of the: present invention that the tetraesters(V), tetracarboxylic acids (VI) and dianhy- 35 drides (Vll) disclosedabove can be used to prepare poly-(imidazopyrrolones) (Xll).Specifically, V, V]. or Vll, or mixtures thereof, when dissolved in asuitable solvent, react with bis(ortho-phenylene diamines) (Xl) toprovide useful polymers (Xll). Using the tetraester 4 (Ill) of thisinvention for illustration, this reaction proceeds as follows:

coon NH I N R" N I ER", HQN NHZ N\ non H 0 ll 2 R N N \N n n 2 N N R Xllent of between about i and about carbon atoms, NH-. or a covalent bond.

This reaction is conducted by contacting a tetraester (V),tetracarboxyiic acid (IV) or dianhydride (V), with thebis-(ortho-phenylcne diamine) (Xi) in the presence of polyphosphoricacid and a condensation-promoting solvent (if desired) at a temperatureof between about 50C. and about 250C, and preferably between about 75C.and about 200C. Suitable solvents for this reaclion includedlmethyllormamlde, N,N- diniethylaeetnnilde. N-mcthylpyrroildone,dlmetliyl sulfoxide. hexamethylphosphornmide, and the like. The reactionnormally requires extended periods of heating. after which time themixture is cooled and the resulting solid recovered by conventionalmeans, e.g., by filtration.

The number of structural units in the polymer chain (i.e.. the polymerchain length) is determined by the value ofn, which value is in turnreflected by the inherent viscosity of the polymer. Generally,polyimidazopyrrolones) (Xll) produced according to the present inventionhave inherent viscosities of between about 0. l 5 and about 3.0, andpreferably between about 0.16 and about 2.0. These inherent viscositiesare determined on solutions of 0.1 gram of polymer/100 milliliters 97% H50 at 25C.

As shown in the foregoing equation. when a tetraester (V) is employed asthe starting material, byproduct alcohol and water are formed. On theother hand, when a tetracarboxylic acid (VI) or dianhydride (Vll) isemployed, only by-product water is formed.

The identity of the end-groups of the poly- (imidazopyrroiones) (Xll) ofthe present invention depend upon the relative proportions of XI and V,Vi, or Vll. Thus, if an excess of Xi over V, VI, or Vll is employed, thepoly(imidazopyrrolones), (Xll) will be substantially capped withortho-phenylene-diamine substituents. if, on the other hand, an excessof V, V], or Vll over X] is used, then X" will be capped withpyrrole-3.4-diester substituents, pyrroie-3,4-dicarboxylic acidsubstituents. or pyrroie-3.4-anhydride substituents, respectively.

It is a further feature of the present invention thatpoiy-(imidazopyrrolones (Xll) can be produced by applying a solution ofXI and V, VI,- or V", or mixtures thereof in a suitable solvent (e.g.,of the type described above) onto a surface and subsequently heating orbaking the surface at the above-indicated temperatures to effectpolymerization and to remove solvent. in this way. there is obtained auseful and desirable film or coating of Xll on the aforementionedsurface.

Both the polyimides and the poly(imidazopyrroloncs) of this inventionare useful for the formation of filaments, fibers. films, and cast andcompressed shaped articles, both solid and poromeric, such as coatings.gaskets, rods. and separators, which are useful for special hightemperatures applications. methods for formation of these articles beingwell known by those skilled in the art. Examples of such products aregaskets and separators in high temperature pumping of liquids anticompressing of gases. baffles and impellers in mixing of liquids.separators in chemical instrumentation, and coatings for electricallines and pipes.

The polyiniides of this invention are especially useful for formingstrong and structurally stable fibers and films which can withstandtemperatures of450-500C. with negligible decomposition. Polymers whichare useful at temperatures as high as 500C. are few in number andextremely valuable for various uses, including coatings for hightemperature surfaces which are encoun tered in rocketry, chemicalprocessing and instrumen tation.

The products and processes of the present invention are illustrated (butnot limited) by the following specific examples.

EXAMPLE I 'grams (4.0 moles) of sodium methoxide and 6 liters ofbenzene. Five hundred and twenty grams (4.0 moles) of ethyl acetoacetateare then added through the dropping funnel over a period of one-halfhour. During the addition, the reaction mixture thickens and the temperature rises from 24C. to 35C. Three liters of benzene are added duringthe course of the addition of the ethy acetoacetate in order to keep themixture stirrable. Tilt system is then heated to reflux, and 550 ml. ofa ben zene-methanol azeotrope are removed. The thick white slurry isthen cooled to C., and 556 grams (4.( moles) of iodine are added insmall portions over a two-hour period.

The mixture is allowed to stand overnight and ther filtered to removethe sodium iodide. The filtrate i: evaporated to a brown, viscous oil.The oil is dissolvec in a minimum amount of boiling absolute ethanol.ant on cooling a white solid precipitates. The solid is re crystallizedtwice from absolute ethanol to give 24( grams of diethyl2,3-diacetyisuccinate.

EXAMPLE 2 Preparation of p-amino-p'-(3,4-dicarbethoxy-2,5dimethylpyrryl) biphenyl To a 500 milliliter, three-neck flask equippedwith z stirrer, reflux condenser, and Dean-Stark trap. 21ft added 45.0grams (0.175 mole) diethyi 2.3-diacetyl succinate, 30.6 grams (0.175mole) benzidine and lOl milliliters glacial acetic acid. The mixture isstirred a reflux for 16 hours, and then cooled. The cooled reac tionmixture is poured into water and neutralized witl sodium bicarbonate. Agolden-brown solid precipitate and is collected by filtration. Theinfra-red and nuclea magnecticresonance spectra of this solid materialcon firms its structure as that of p-amino-p'-(3,4dicarbethoxy-2,S-dimethylpyrryl)biphenyl. Yield: 40 grams l00% of theorybased on either benzidine or di ethyl 2,3-diacetylsuccinate).

EXAMPLE 3 19 EXAMPLE 4 Preparation of p.p'-bis(3.4-dicarbethoxy-2.5-dimethylpyrryl) biphenyl:

To a 500 milliliter. three-neck flask. equipped with a stirrer. refluxcondenser. and Dean-Stark trap. are added 45.0 grams (0.i75 mole)diethyl 2.3- diacetylsuccinate. 14.0 grams (0.08 mole) benzidine and lmilliliters glacial acetic acid. The mixture is stirred at reflux for l6hours. then cooled. A solid precipitates and is removed by filtrationand dried. The flltrntc is poured into water. and the solution isneutralized with sodium bicarbonate. A solid precipitate is collectedand is found to be identical to the precipitate obtained from the aceticacid. Both solids are combined for a total yield of 51.5 grams (100% oftheory based on benzidine) of p.p"bis(3.4-dicarbethoxy-2,5-dimethylpyrryl) biphenyl.

Analysis Calculated: C 65.l2; H. 4.65. N. 5.43

for C H OM, found: C 64.4 H 4.71; N 5.45

EXAMPLE 5 Preparation of p,p'-bis(3,4-diearboxy-2.5-

dimethylpyrryl) biphenyl:

To a 500 milliliter. three-neck flask equipped with stirrer andDean-Stark trap with condenser are added 51.5 grams (0.08 mole)p,p'-bis(3,4-dicarbethoxy-2,5- dimethylpyrryl) biphenyl and 250milliliters of 95% aqueous ethanol. The mixture is heated to reflux todissolve the tetraester, and 16 grams (0.4 mole) of sodium hydroxide areadded to effect hydrolysis. in a few minutes a brown precipitate isformed which is redissolved by the addition of a small amount of water.The ethanol is removed by azeotropic distillation while the liquid levelis maintained by the addition of water to the reaction flask. When nomore ethanol remains, the brown, aqueous residue is treated withdecolorizing charcoal and acidified by the addition of HCl to give atancolored precipitate. This solid is filtered off and dried in a vacuumoven. Yield: 41.3 g. 100% of theory). The infra-red spectra of thiscompound shows that saponification has occurred to give thetetracarboxylic acid, p.- p'-bis( 3,4-dicarboxy-2,S-dimethylpyrryl)biphenyl.

EXAMPLE 6 Preparation of p,p'-bis(3.4-dicarboxy-2,5- dimethylpyrryl)biphenyl. dianhydride:

into a one-liter flask, equipped with a reflux con denser and dryingtube are charged 41.2 grams (0.08 mole) ofp.p'-bis(3,4-dicarboxy-2,S-dimethylpyrryl) biphenyl from Example 3 and500 milliliters of acetic anhydride. The mixture is heated to reflux for48 hours, then cooled. A solid precipitate is removed by fiItration,washed three times with ethyl ether. and dried in a vacuum oven. Theyield is 32.6 grams (85% of theory). The infra-red spectrum of thismaterial is compatible with the structure of the dianhydride of p,p'-bis(3.4-dicarboxy-2.S-dimethylpyrryl) biphenyl.

EXAMPLES 7 AND 8 Preparation of other dianhydrides: in a similar manner.other tetraesters of the present invention are prepared in which thebenzidine is replaced by p-phenylenediam|ine. ethylenediamine anddi-(paraaminophenyl) ether. hydrolyzed and then dehydrated to thedianhydrides. The infrared spectra of the resulting dianhydrides arecompatible with the proposed structures for these compounds.

EXAMPLE 9 Preparation of poly-(amic acid) from benzidine andp.p'-bis(3.4-dicarboxy-2.S-dimethylpyrryl) biphenyl. dianhydride:

To a 500 milliliter flnsk equipped with stirrer and reflux condenser areadded 10.8 grams of p.p'-bis(3.4- dicarboxy-2.S-dimethylpyrryl)biphenyl. dianhydride from Example 4. 4.6 grams benzidine and I00milliliters dimethyl formamide. The mixture is stirred for five hours at40-75C.. then allowed to stand at room temperature for about 72 hours. Asolid material is removed by filtration and washed three times withwater and dried in a vacuum oven at l40C. Yield: 13.5 grams of agolden-brown solid which is soluble in 97% H The infra-red spectrumindicates that this material is a polymer containing both amide andcarboxylic acid substituents. The product also contains some polyimide.

Analysis Calculated for:

(C H O NJ C 72.3; H 4.8; N 8.45 poly(amic acid) (C ,H O N C 76.5; H 4.5;N 8.95 polyimide Found: C 72.4; H 5.2; N 8.95

inherent viscosity (0.] g/l00 ml 97% H 80 at 25C.) 0.39.Thermogravimetric analysis shows a 0.15% weight loss up to 325C. andthen levels off with no further weight loss until 460C.

EXAMPLE [0' A sample of the polymer product from Example 9 is heated inrefluxing N.N-dimethylacetamide at l60C. for five hours and shows asimilar yield of a product having the following analysis: C 76.5; H5.72; N8.45. The infra-red spectrum is compatible with the poly imidestructure. The polymer has an inherent viscosity (0.l g/lOO ml 97% H 50at 25C.) of 0.29. Thermogravimetric analysis shows only a small weightloss up to 470C.

in a further experiment, the reaction of Example 9 is repeated exceptthat the reaction is conducted at 100C. Analysis of the resultingproduct indicates that it is substantially polyimide.

EXAMPLES ll-l4 The same procedure as in Example 10 is-used in preparingother polyimides using the analogous diamine compounds for values of R"and R' as shown in Table l below. The percent conversions indicateuseful reac tivities, and analysis for carbon. hydrogen. and nitrogen inthe products indicate that the thecretical reactions are closelyfollowed. The inherent viscosities in 97% sulfuric acid at 25C. indicategood clarity in solution. Thermogravimetric analyses show thetemperatures at which these polyimides suffer 5% weight loss. All indicate utility in high-temperature applications.

ARYL COMPONENTS OF DIAMINES POLYMERIZATION CONDYTIONS Ex. R R' SolventTemp. Conv. '4' No. C.

l I N.N-

dimethyl I60 89 acctamidc O O n u u l. dimcthyl S S lormamide I50 96 u nO O N.N- l3 Q dimclhyl I30 )8 acetamide N.N- I 4 dimcthyl I30 87acetamide POLYIMIDE FT. 7c COMPOSITION OF POLYIMIDES ANALYSIS CalculatedAnalyzed TGA Anal- LV. ysis C H N O H N Ex. wt No loss) II 0.29 470C.76.4 4.5 8.93 76.5 5.72 8.87 II 0.38 455 63.4 3.7 7.4l 62.8 4.1 7.23 I}0.48 440 72.8 4.3 8.48 68 4.35 8.05 14 0.16 420 69.4 5.8 11.58 67.7 5.4210.4

EXAMPLE 15 Preparation of a poly'(imidazopyrrolone from p,p'-bis(3,4-dicarboxy-Z-dimethylpyrryl) biphenyI and 3,3- diaminobenzidincTo a 500 milliliter flask equipped with a stirrer and reflux condenserare added 10.8 grams of p,p-bis(3,4- dicarboxy-Z,S-dimethylpyrryl)biphenyI, 5.4 grams of 3.3-diaminobenzidine. and 200 grams of polyphos-The invention has been described herein with reference to certainspecific aspects. However, the invention is not to be considered aslimited thereto as obvious variations will occur to those skilled in theart.

We claim:

I. A polyimide consisting esentially of recurring units of the formula:

N N :I!

. "Inherent viscusiilcs determined on ((1.1 gram of sumple)/( I00milliliter 9754 H SOJ at 25C.

wherein R is H or an allkyl substituent of between about I and about 10carbons; and R" is an arylene substituent, biarylene substituent ordiarylene substituent, and the inherent viscosity of said polyimide isbetween about 0.15 and about 3.0 as determined with solutions of O.Igram of polymer/I00 milliliters 97% H at 25C.

2. The polyimide according to claim 1, wherein R is a lower alkylsubstituent of between about I and about 6 carbon atoms.

3. The polyimide according to claim 2 wherein R is methyl and R" isphenylene, biphenylene, diphenylene ether, diphenylene sulphone ordiphenylene amine.

4. The polyimide according to claim 3 wherein R" is biphenylene and theinherent viscosity is between about 1.5 and about 3.0 as determinedwith'solutions of 0.l gram of polymer/I00 milliliters 97% H 80 at 25C.

5. The process for producing a polyimide of claim I, which comprisesheating a N-substituted pyrrole-3, 4- diester having the formula:

ROOC

wherein R is a lower alkyl substituent of between about I and about 6carbon atoms; R is H or an alkyl substituent of between I and about l0carbon atoms; and R" is an arylenc substituent. biarylene substituent ora di- 8. The process according to claim 7 wherein the inert high-boilingsolvent is dlmcthylt'ormamldc. N.N- dimethylacetamide, dimethylsulfoxide. hexamethylphosphoramide or an aromatic hydrocarbon.

9. A process for preparing a polyimide having an inherent viscosity ofbetween about 0.15 and about 3.0. as determined with solutions of 0.1gram of polymer/lOO milliliters 97% H 80 at 25C., said polyimideconsisting essentially of recurring units of the formula said processcomprising heating a mixture of about equamolar amounts of a2.3-diacylsuccinic diestcr of the formula RI I C aooc :00 c&

and a diamine of the formula NH,-R"NH at a temperature of between aboutC. and about 300C, wherein said temperature is above the melting pointof the corresponding N-substituted pyrrole 3,4- diester for a timesufficient to form a polymer where, in the above formula. R is anorganic ester forming substituent of between one and ten carbon atoms, Ris H or an alkyl substituent between about 1 and about 10 carbon atomsand R" is an arylene substituent, biary lene substituent, or a diarylenesubstituent.

sass:

1. A POLYIMIDE CONSISTING ESENTIALLY OF RECURRING UNITS OF THE FORMULA:2. The polyimide according to claim 1, wherein R'' is a lower alkylsubstituent of between about 1 and about 6 carbon atoms.
 3. Thepolyimide according to claim 2 wherein R'' is methyl and R'''' isphenylene, biphenylene, diphenylene ether, diphenylene sulphone ordiphenylene amine.
 4. The polyimide according to claim 3 wherein R''''is biphenylene and the inherent viscosity is between about 1.5 and about3.0 as determined with solutions of 0.1 gram of polymer/100 milliliters97% H2SO4 at 25*C.
 5. The process for producing a polyimide of claim 1,which comprises heating a N-substituted pyrrole-3, 4-diester having theformula:
 6. The process of claim 5 wherein the product is held at thereaction temperature for from about 30 minutes to about 10 hours.
 7. Theprocess according to claim 5 wherein said heating is conducted at atemperature of between 150*C. and about 200*C. in an inert condensationpromoting, high-boiling solvent which is liquid at said indicatedtemperatures.
 8. The process according to claim 7 wherein the inerthigh-boiling solvent is dimethylformamide, N,N-dimethylacetamide,dimethyl sulfoxide, hexamethylphosphoramide or an aromatic hydrocarbon.9. A process for preparing a polyimide having an inherent viscosity ofbetween about 0.15 and about 3.0, as determined with solutions of 0.1gram of polymer/100 milliliters 97% H2SO4 at 25*C., said polyimideconsisting essentially of recurring units of the formula